From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by mail.toke.dk (Postfix) with ESMTPS id 7E67CA3969C for ; Thu, 2 Nov 2023 23:58:51 +0100 (CET) Authentication-Results: mail.toke.dk; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20230601 header.b=lpcJGjZl Received: by mail-pj1-x104a.google.com with SMTP id 98e67ed59e1d1-28032570a00so1311781a91.0 for ; Thu, 02 Nov 2023 15:58:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1698965930; x=1699570730; darn=xdp-project.net; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=HxShEwzn2SwGeh/fxMP8q3kc87+t2JtKbOUp4FoNDAk=; b=lpcJGjZlt5fjxW5oXCfqN2jqK02buqtxH/FwYIuvRA7EvzOAuFGW0w6jEdZcZXUzot JoA+ik3PSRfy9FEfHMIN657KBvfjzydIwj6NfhEdPoRXbzl/KAwPj7Pm4EAyq/7UxiPk xgOoKiEFXgJJzSs0z69iln9rQKQsDkVVPJypV6+hq2sa1jMgsXFH0XyP8sL51aYHGsFF ps8jRiGjfR20b2CM/8A72ITAkEqR0XMEOKJubKUVK1QVYTAFCaSvcMzq8IJVw4SQkhu9 KKtP7zwBAj23idYo2ZGIr2tiFSm+/Y3pj1U8+1bgTikqwvdzrkZMFbNyBeW81Uoc6uWE Qj5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1698965930; x=1699570730; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=HxShEwzn2SwGeh/fxMP8q3kc87+t2JtKbOUp4FoNDAk=; b=uNW1Kts/l/n/S0bK3zONWpZNZQawiX67lE7ryiWjF+gVnc6PErJJ8zRVNEAAu4Vgsy xeB0DB13oVV+tNfI6UtjOdMk76EefufOuNmCrRAVGYi3K9bQ0T8rC4xcuFa6YxKn7nnJ vrjGVoIupJzjp/PFVc51TiB0M+nHVjRcUhCUki0SDNwD/rer8nMfkP19oif2RNnH5y2P 7eV1868vmNV+iSRflSQpFAd5R1BIRjFeJZwN6WgVypuiFxhdPItHqTEtzx0wu9U/lVp2 w441xjyjFKc0lhCa5CFNMVOfIh5b9bzGV79KzZeZ7AN5ZbRgufT7DzpM7VLbPvYet9KC MRgA== X-Gm-Message-State: AOJu0YxC6/Zuyy472idJu+CkkLnI7VNXfNHK8I6ontqY3gZ4yObqUcq1 AjEybDCfUOU4rNdIa/h6QUadLaw= X-Google-Smtp-Source: AGHT+IFHksWobVq1DgklW4mDeMreDlgWsTTNqA/kCtQ42AoUqzv4G7g6ZHTYaGfKWIPjKCcaSl6uF+I= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a17:902:d48c:b0:1cc:2f2a:7d33 with SMTP id c12-20020a170902d48c00b001cc2f2a7d33mr319925plg.2.1698965929763; Thu, 02 Nov 2023 15:58:49 -0700 (PDT) Date: Thu, 2 Nov 2023 15:58:30 -0700 In-Reply-To: <20231102225837.1141915-1-sdf@google.com> Mime-Version: 1.0 References: <20231102225837.1141915-1-sdf@google.com> X-Mailer: git-send-email 2.42.0.869.gea05f2083d-goog Message-ID: <20231102225837.1141915-7-sdf@google.com> From: Stanislav Fomichev To: bpf@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: YDZVOPANMI7KG4N5MDA4NQWMXR3UAWMH X-Message-ID-Hash: YDZVOPANMI7KG4N5MDA4NQWMXR3UAWMH X-MailFrom: 3qSlEZQMKCT4xiklttlqj.htr2iu-mnsyx2iu-uwtojhy.sjy@flex--sdf.bounces.google.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, kuba@kernel.org, toke@kernel.org, willemb@google.com, dsahern@kernel.org, magnus.karlsson@intel.com, bjorn@kernel.org, maciej.fijalkowski@intel.com, hawk@kernel.org, yoong.siang.song@intel.com, netdev@vger.kernel.org, xdp-hints@xdp-project.net X-Mailman-Version: 3.3.8 Precedence: list Subject: [xdp-hints] [PATCH bpf-next v5 06/13] xsk: Document tx_metadata_len layout List-Id: XDP hardware hints design discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: - how to use - how to query features - pointers to the examples Signed-off-by: Stanislav Fomichev --- Documentation/networking/index.rst | 1 + Documentation/networking/xsk-tx-metadata.rst | 70 ++++++++++++++++++++ 2 files changed, 71 insertions(+) create mode 100644 Documentation/networking/xsk-tx-metadata.rst diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst index 683eb42309cc..a297a894b366 100644 --- a/Documentation/networking/index.rst +++ b/Documentation/networking/index.rst @@ -123,6 +123,7 @@ Refer to :ref:`netdev-FAQ` for a guide on netdev development process specifics. xfrm_sync xfrm_sysctl xdp-rx-metadata + xsk-tx-metadata .. only:: subproject and html diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst new file mode 100644 index 000000000000..4f376560b23f --- /dev/null +++ b/Documentation/networking/xsk-tx-metadata.rst @@ -0,0 +1,70 @@ +================== +AF_XDP TX Metadata +================== + +This document describes how to enable offloads when transmitting packets +via :doc:`af_xdp`. Refer to :doc:`xdp-rx-metadata` on how to access similar +metadata on the receive side. + +General Design +============== + +The headroom for the metadata is reserved via ``tx_metadata_len`` in +``struct xdp_umem_reg``. The metadata length is therefore the same for +every socket that shares the same umem. The metadata layout is a fixed UAPI, +refer to ``union xsk_tx_metadata`` in ``include/uapi/linux/if_xdp.h``. +Thus, generally, the ``tx_metadata_len`` field above should contain +``sizeof(union xsk_tx_metadata)``. + +The headroom and the metadata itself should be located right before +``xdp_desc->addr`` in the umem frame. Within a frame, the metadata +layout is as follows:: + + tx_metadata_len + / \ + +-----------------+---------+----------------------------+ + | xsk_tx_metadata | padding | payload | + +-----------------+---------+----------------------------+ + ^ + | + xdp_desc->addr + +An AF_XDP application can request headrooms larger than ``sizeof(struct +xsk_tx_metadata)``. The kernel will ignore the padding (and will still +use ``xdp_desc->addr - tx_metadata_len`` to locate +the ``xsk_tx_metadata``). For the frames that shouldn't carry +any metadata (i.e., the ones that don't have ``XDP_TX_METADATA`` option), +the metadata area is ignored by the kernel as well. + +The flags field enables the particular offload: + +- ``XDP_TXMD_FLAGS_TIMESTAMP``: requests the device to put transmission + timestamp into ``tx_timestamp`` field of ``union xsk_tx_metadata``. +- ``XDP_TXMD_FLAGS_CHECKSUM``: requests the device to calculate L4 + checksum. ``csum_start`` specifies byte offset of where the checksumming + should start and ``csum_offset`` specifies byte offset where the + device should store the computed checksum. + +Besides the flags above, in order to trigger the offloads, the first +packet's ``struct xdp_desc`` descriptor should set ``XDP_TX_METADATA`` +bit in the ``options`` field. Also note that in a multi-buffer packet +only the first chunk should carry the metadata. + +Querying Device Capabilities +============================ + +Every devices exports its offloads capabilities via netlink netdev family. +Refer to ``xsk-flags`` features bitmask in +``Documentation/netlink/specs/netdev.yaml``. + +- ``tx-timestamp``: device supports ``XDP_TXMD_FLAGS_TIMESTAMP`` +- ``tx-checksum``: device supports ``XDP_TXMD_FLAGS_CHECKSUM`` + +See ``tools/net/ynl/samples/netdev.c`` on how to query this information. + +Example +======= + +See ``tools/testing/selftests/bpf/xdp_hw_metadata.c`` for an example +program that handles TX metadata. Also see https://github.com/fomichev/xskgen +for a more bare-bones example. -- 2.42.0.869.gea05f2083d-goog